Planet carrier assemblies have a cage or spider in which a plurality of pinion gears are rotatably mounted. One or more thrust bearings are positioned between each gear and the inner sidewall surface of the cage to accommodate relative rotation between the pinion gears and the cage. These washers also absorb thrust forces imposed on the pinion gears.
When two thrust washers are positioned on each side of each gear, the washer adjacent the cage is usually held stationary relative to the cage and the washer adjacent the gear is permitted to rotate. When a single thrust washer is used on each side of each gear, the cage sidewall, as well as the gear sidewall, must be machined to accommodate rotation of the washer relative thereto. When two adjacent are used, the assembler has the task of ensuring each pinion gear has a total of four washers. If four pinions are mounted in the cage, the assembler must account for sixteen washers. If a single washer is omitted, at least one pinion of the planet carrier must be disassembled so that the washer can be installed. Since the pins are swaged at assembly, a new pin is required when the pinion is reassembled.
When a single washer is installed on each side of each pinion gear, the cost of additional machining increases the cost of the carrier assembly. Each cage sidewall must be inspected to ensure that the machining has been accomplished prior to assembly of the cage. When two washers are used on each side of each pinion, the stationary washer must have a tab or other structure which will prevent rotation between the cage and the stationary washer.